<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer{
            width:800px;
            /* height:300px; */
            padding:10px;
            margin:10px auto;
            border:10px solid red;
            background-color: gray;
        }
        .inner{
            float:left;
            width:300px;
            height:300px;
            margin:10px;
            border:1px solid black;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner">

        </div>
        <div class="inner">

        </div>
    </div>
</body>
</html>